Shake screen with phasing links and air cushions



Oct. 10, 1961 E. N. WOOD 3,003,635

SHAKE SCREEN WITH PHASING LINKS AND AIR CUSHIONS Filed Aug. 7, 1959 3 Sheets-Sheet 1 IN V EN TOR.

Oct. 10, 1961 v E. N. woon 3,003,635

SHAKE SCREEN WITH PHASING LINKS AND AIR CUSHIONS Filed Aug. 7, 1959 3 Sheets-Sheet 2 l I 36 I /2 /2 E i 26 26 i f 5i 'IIIIII- Oct. 10, 1961 E. N. woon 3,003,635

SHAKE SCREEN WITH PHASING LINKS AND AIR CUSHIONS INVEN TOR.

United States Patent 3,003,635 SHAKE SCREEN WITH PHASING LINKS AND AIR CUSHIONS Everett N. Wood, Cedar Rapids, Iowa, assignor to Pettibone Mulliken Corporation, a corporation of Delaware Filed Aug. 7, 1959, Ser. No. 832,360 13 Claims. (Cl. 209415) A popular type of screen for classifying (sifting) loose material such as crushed stone is a type known as a horizontal screen. The preferred forms of horizontal screen have been shaken or oscillated with an oblique action which not only bounced the pieces into the air, but also bounced them somewhat towards the discharge end of the screen. Pieces large enough to be retained by a given screen would ultimately be discharged at the discharge end, while the smaller pieces would work down through the larger pieces and through the screen. A common manner of producing the oscillations is to drive a pair of eccentrically weighted shafts in opposite directions and in phase with one another so that the forces produced are balanced except for a force plane or plane of action perpendicular to the plane common to the axes of the two shafts. It has been common practice to attempt to confine the movements of the screen to movements parallel with this plane of action. If the plane of action lies at 45 to the horizontal, then ideally each point on the screen would oscillate on a line lying at 45 to the horizontal.

This confining of the movement of shake screens has been accomplished heretofore, although never perfectly, by either tie links or tie springs. The most common method has been with tie springs inthe form of leaf springs firmly secured at their lower ends and extending upwardly approximately in planes perpendicular to the force plane. Such leaf springs have been very trouble some, especially because of frequent breakage.

Tie links have rarely been used, because from a practical standpoint they had to hang downwardly in order to provide the necessary lateral stability. The downward hanging of tie links has never been popular, partly because of increased cost without gain, and partly because in some positions they would obstruct access to the screen. Upwardly extending tie links are shown in at least one patent, but it is doubted that they were ever successfully used.

According to one aspect of the present invention, up wardly extending tie links may be used. The necessary lateral stability is provided by providing adequate bearing spread in the axial direction (which is transversely of the screen). In the preferred form of the invention, this stability is combined with a phasing feature by rigidly connecting tie links on opposite sides of the screen with one another by means of a torque tube or phasing tube, to form a rigid U, with the bearings (preferably rubber bushings) as far apart as the supporting framework permits, somewhat farther apart than the width of the screen. This aspect of the invention is the subject matter of abandoned application, Serial No. 716,802, filed February 21, 1958.

The phasing links have proved to be extremely advantageous. It seems to prevent most of the wild or unuseful vibrations previously a well-known phenomenon of horizontal screens. The difference can be detected in part by the extent to which the old screen and the new shakes the fioor when the two screens are operated in a building. With the leaf spring mounted screen the shaking of the floor can hardly escape notice. With a screen of this invention the shaking of the floor is more likely to be barely perceptible if attention is paid to it, or perhaps not even then.

Another aspect of the present invention is concerned 3,063,635 Patented Oct. 10, 1961 in part with a phenomenon known as squatting. Horizontal screens prior to the present invention have commonly been supported by coil springs. Most commonly these springs have been disposed in the intended line of action and located directly under the upper ends of either the leaf springs or the tie links, whichever was used. These springs ordinarily could be adjusted and were so adjusted that when the horizontal screen was operating under its intended load its confining means, whether links or springs, would operate an equal distance above and below the position in which they formed a straight line perpendicular to the intended line of action. However, if an exceptionally heavy load should be dumped upon the screen, it would squat. By this is meant that it would be pressed down by its extra weight to a lower mean position. With leaf springs this was exceptionally objectionable because it would result in greater spring distortion. Instead of a given amount of movement being divided equally between movement downward from the neutral position of the spring and upwardly from the neutral position of the spring, a greater portion of it or all of it would be downwardly from the neutral position of the spring. This was one of the factors that contributed to the rapid failure of these springs. It also contributed to other undesirable effects such as the transmission of vibration to the supporting structure, partly because the movement would no longer be so close to the ideal in direction. Of course, with either leaf springs or links the movement is not a straight line movement but more nearly an arcuate movement. A straight line movement in the direction that the force of the eccentric pair acts would be ideal. An arcuate movement with only slight movement both above and below the position at which the movement is parallel to or tangent to the line of such force results in the minimum departure from this line. Squatting would result in greater departure from the line of force, and hence greater departure from the ideal line of movement.

According to the present invention, the coil springs are replaced by air cushions, which could also be called air springs. One advantage of this is that the air springs resists squatting better than the coil springs which have been used heretofore. Where the ordinary helical coil spring exerts a force on the compressing member which is proportional to the amount of compression, the air cushion, as it is compressed successively further and further, builds up the force applied to the compressing member more and more rapidly.

Another advantage of the air cushions in the use in question is obtained best when the air cushions are used with links, preferably the phasing links of the present invention. With these, a slight amount of squatting is practicably unobjectionable. With leaf springs any squating probably reduced the life of the leaf springs. With the present invention the small amount of squatting which ordinarily is permitted by the air cushions causes no decrease in the life of the parts. In other words, the air cushion and phrasing links cooperate to provide exceptionally smooth and long life action because the air springs reduce the squatting and the phasing links make this reduced degree of squatting almost unobjectionable.

Additional advantages and objects of the invention will be apparent from the following description:

Designation of figures 3 FIGURE 4 is a sectional view through the air cushion taken approximately on the line 44 of FIG. 2.

FIGURE 5 is a sectional view through the gear case of FIG. 1.

FIGURE 6 is a sectional view through the eccentric shaft housing showing especially the oil vent.

General description Although the following disclosure offered for public dissemination is detailed to ensure adequacy and aid understanding, this is not intended to prejudice that purpose of a patent which is to cover each new inventive concept therein no matter how others may later disguise it by variations in form or additions or further improvements. The claims at the end hereof are intended as the chief aid toward this purpose, as it is these that meet the requirement of pointing out the parts, improvements, or combinations in which the inventive concepts are found.

The invention has been illustrated in conjunction with a horizontal shaking screen or shake screen. Horizontal screens are well known. Such a machine conventionally includes a base 11 by which a screen unit 12 is carried in a manner permitting a planned oblique reciprocatory movement of the screen unit 12. Screen unit 12 might commonly include a plurality of screens. For example there may be a coarse screen 13 at the top, a medium screen 14 at the lower level, and a fine screen 16 at the lowest level. The material is fed onto the coarse screen 13 at the feed end shown at the left, and the various sizes are separately discharged. The screen unit is shaken in a manner to bounce the burden of the screens toward the discharge end of the unit shown at the right. The sizes retained by the various screens are each discharged over the discharge ends of the screens. The size which passes through the bottom screen may be collected beneath the screen in any suitable manner.

In the illustrated form of screen unit, a sloping feed plate 18 is provided at the feed end onto which the mate rial is initially dropped by a feeding conveyor or the like. The shaking of this plate as part of the screen unit tends to produce a preliminary classification of the material which reduces wear on the screen and permitsthe use of a'somewhat shorter screen area. The illustrated screen unit also includes side shields 19 at the feed end, which may be removable for access under a feeding conveyor which might project down to their level.

Phasing link mounting According to the present invention, movement of the screen unit 12 is confined to the desired movement by four tie links 26 of special torsion or phasing construction to be described.

The construction of the phasing link assemblies are best Seen in FIG. 3. Each tie link 26 is welded to the end of a phasing or torque tube 27. Gusset plates 28 are preferably provided. The torque tube and tie link are jointly pivoted at each end of the torque tube to base 11, preferably by a construction such as that clearly shown in FIG. 3. Likewise each tie link 2s is pivoted to the side of screen unit 12 by a similar construction clearly seen in FIG. 3.

In each instance the pivotal connection shown is achieved with the aid of a rubber bushing 31 lying between a fixed bushing 32 and a surrounding pivotal bushing 33. A hearing construction would be equally suitable except that in the vicinity of a screen there is some difficulty in keeping bearings free from dirt and well lubricated.

The internal bushings 32 may be welded to the plates on which they are mounted or they may be secured thereto firmly by bolts 34 and 36.' Bolts 34 are made quite rigid in their positioning by braces 35 welded to base 11. For access to bolts'34, openings 37 are provided in tube 27, and these openings have been shown as reinforced,

4 The bolt 36 extends through a reinforcing plate 38 as Well as through the main plate of screen unit 12.. Bushings 39 (which may be of red vulcanized fiber) surround bolts 34 and 36 to seal the area where scouring might otherwise occur.

Suspension springs As best seen in FIG. 2 the unit 12 is held at the desired medial height at rest by air springs or air cushions 41. Preferably the height at which the unit 12 is held is adjustable by varying the inflation of the air cushions 4-1 through valve stem 42. Air cushions 41 bear on brackets 43 which are braced by gusset plates 44. Some of the advantages of the phasing links are attained even if metal springs are used instead of air springs 41. Either may rest on footing 45 carried by beam 11.

Eccentric shaker drive The screen unit 12 is preferably shaken by an eccentric drive unit 46 which is a mass reaction means and is carried by extension plates 47 mounted on the side of screen unit 12. This portion of the side of screen unit 12 may be stiffened by stiffener plates 48. Extension plates 47 are preferably in facing contact with or in alignment with the sides of screen unit 12 to transmit thrust in a substantially straight line.

The drive unit 46 conventionally includes two oppositely rotating in-phase eccentrically weighted shafts so that all forces are balanced out except as to forces in the force plane or plane of action perpendicular to the common axial plane and midway between the axes. The shaft for one of the two eccentrics is driven by belts as illustrated. The motor 51 may be mounted on the base 11, as on a shelf extending therefrom.

Although difierent designers have different ideas as to the preferred angle of oscillation of the screen unit 12, the plane of tie arms 56 should be perpendicular to the chosen angle of oscillation and the common axial plane for the two eccentrics 46 should also be perpendicular to the chosen plane. At present it is preferred that the plane of oscillation be 45 from the vertical, and accordingly the plane of tie tubes 26 and common axial plane of unit 46 are also at 45, although these latter two are inclined oppositely to the force plane. it is desired that the unit 46 be positioned along the length of screen unit 12 at such point that its force plane extends substantially ahead of the center of gravity of the unit 12, that is nearer to the feed end. The loading of the screen unit 12 is usually considerably heavier at its feed end and therefore the preferred location places the plane of action close to the center of reaction, considering both the screen unit and its load.

Best results are usually attained if the air cushions 41 are so adjusted by inflation that tie links 26 will oscillate equally in both directions from a neutral plane perpendicular to the plane or line of force exerted by the driving unit, which is the intended planeof action of unit 46. However, one of the advantages of the tie link construction as compared to prior tie springs (either leaf springs or hickory springs) is that the need for accurate adjustment of spring units 41 is less severe. Tie springs, especially the steel leaf springs commonly used heretofore in the shaker screen art, broke frequently, due to fatigue. Naturally if they oscillated about their position of repose they would be expected to last longer than if they did the same amount of oscillating about a flexed position, because in one direction the amount of distortion when in the neutral plane would be added to the distortion of oscillation. Spring life is greatly shortened by repeated fleidng beyond safe amounts.

The freedom from need-for accurate adjustments permits an operator to experiment with different angles of action of the screen unit 12 by adjusting the spring units 1, without danger of causing rapid spring destruction.

Although provision may be made for inflating or deflating air cushions 41 automatically, for raising or lowering the neutral plane to the predetermined level, as the load on the screen varies, this has been found unnecessary. Ordinary load increases do not cause much squatting when air springs are used, and the phasing links make minor squatting harmless.

Lateral rigidity The illustrated construction serves not only the function of ensuring that the two sides of the screen operate in phase with one another, but also that of preventing side sway and lateral components of oscillation. The illustrated form is preferred, even aside from the fact that it also ensures in-phase operation of the two sides, because it gives full width bearing spread and still only requires the minimum cost of only one hearing (or rubber bushing) at each end of each tie link.

It is to be observed that some modifications could prevent the side sway without safeguarding against out-ofphase operation between the sides. It is conceivable that the out-of-phase operation between the sides would not prove to be as objectionable with the tubular tie link construction here suggested, as it has in the past, with the spring type construction. Furthermore, with extreme care in the placing of the drilled holes for the various parts to get perfect parallelogram operation, exactly alike between the two sides, the out-of-phase difficulty might prove to be largely avoidable even without the phasing or torque tube connection between links 26 on the two sides.

If the out-of-phase difficulty is to be dropped from consideration, the required sturdiness against side sway could be provided by providing each tie link 26 at the fixed-axis end thereof with hearing means or rubber bushing means having a suflicient bearing spread in the axial direction to provide this rigidity. With the inherent resiliency of the rubber bushings which are preferred for reasons already indicated, a wider spread would probably be needed than with very snugly fitting non-resilient bearings. At present it is preferred that with rubber bushings the bearing spread be at least equal to the length of the arm, but probably experience will show that this can be shortened somewhat. Of course, the bearing spread could theoretically be provided at the other ends of tie links 26, but the natural place is at the fixed axis ends of tie links 26 because the spread can be provided by extension inwardly beyond the sides of the screen unit where it is completely out of the way, and does not enlarge overall dimensions.

High frequency operation For some types of screening a high frequency of oscillation of the screen is desirable. eretofore, the higher frequencies sometimes desired have seemed to be impractical. Even a frequency of 900 rpm. has caused short bearing life in the drive unit. The described structure has been found to operate quite satisfactorily at higher frequencies, no objectionable harmonics developmg.

To operate long at higher frequencies such as 1100 r.p.m., it is necessary to improve the power unit 46 as compared to those previously available, and in fact these improvements are highly desirable even for operation at more ordinary speeds. Although it is possible that the improvements of the power unit will have to be the subject of a separate application, they may be briefly described here order to be sure to comply with the requirement of disclosing the preferred form contemplated.

High speed operation of the eccentric power unit 46 is primarily a matter of adequate bearings and lubrication. Heretofore, the bearings for the upper shaft in the Wall of gear case 51 have not been adequately lubricated and have run hot even at ordinary speeds. According to the present invention, the gears 52 on the two shafts are provided with apertures 53 in their webs to permit airborne oil to pass through them, and enough oil is provided in the gear case 51 so that the air in the gear cases becomes charged with goblets of oil. This has proved to be enough to provide adequate lubrication for the upper bearings, which are roller bearings. This aggravates the problem of adequate venting of the gear boxes, 3. problem which previously had not been adequately solved.

The venting problem is solved by providing a vent conduit for the gear case 51 extending from somewhat above the oil level to the space closed by eccentric housing 56. Thus tube 57 extends to an aperture 58 through the center of the bearing supporting wall 59. Another tube 61 extends from the other end of aperture 58 to a point high in the eccentric shaft housing 56 where it opens into this housing. The housing 56 is not air tight. The lower end of the tube 57 is cut off at a steep taper so that oil will drip from its point, leaving the aperture above the point free for the passage of air. Using a central aperture of the gear casing has an advantage in permitting interchange of parts for different designs, so that the provision of separate righthand parts and left-hand parts is not required even if the gear box 51 is sometimes to be placed at the opposite end. Tube 61 preferably holds a condenser mesh or the like to minimize escape of oil or oil vapor, and housing 56 is provided with a drain plug, since oil should not be allowed to accumulate in it.

Good rotary seals should be provided around the eccentrically weighted shafts, beyond the bearings from the gear case, to retain oil in the gear case, as seen in FIG. 4.

Air cushion units The air cushion units need not be described in great detail inasmuch as they are available on the market. The particular one illustrated is manufactured by Firestone Tire and Rubber Company and is widely used in automobiles as the air ride. An annular casing 71, of flexible reinforced rubber or the like, is sealed to end plates 72 eachhaving a rim 72', and each provided with sealed securing studs 73, and one of which is provided with a valve stem 42 sealed thereto. This air cushion can be installed exactly as furnished, but at present it is preferred to provide on the upper side thereof a shield 76 which preferably is a steel annulus which also serves as a spreader. Thus by limiting the axial flexing of the side wall of the casing with respect to the rims the casing spreads laterally upon being compressed, more quickly than if the spreader were not used. This is believed to enhance the squat-resistance of the air cushion 41.

The shape of the spreader and shield 76 need not be exactly as shown, and that shown may not even be the best. The shape should be such as to so limit the flexing of the casing side walls 79 that the outside diameter of the casing will spread as rapidly as is practicable during the chosen part of the compression stroke. This may be from the neutral position to either the maximum ideal compression (the operating deflection with the intended load) or the maximum compression commonly encountered during operation. It follows that there may be no increase of diameter (efiective area) during the greater deflections such as those encountered in starting.

Although wide variations may be satisfactory, it is perhaps helpful to note that the air cushion found satisfactory has a plate diameter of approximately 5.3 inches and is intended by the manufacturer to operate with the plate spacing varying from approximately 2.0 inches to approximately 6.1 inches. This refers to the spacing between the outer surfaces of the two end plates. Ideal deflection here is only about %1 inch, inch each way.

The resistance to squatting of such an air cushion results from the combined effects of increasing compression of the air as compression occurs and increasing effective area. With one line of screens inflation pressures have been found to be in the range of 42 to 55 lbs. The medium operating pressure under load will be slightly greater than unloaded, and the maximum operating pressure at the end of each compression stroke will be greater. The best practice is to inflate all air cushions uniformly until the normally loaded screen is at the height at Which the links 26 are perpendicular to the plane of force or intended oscillation.

The relatively rapid build up of pressure which resists squatting is also advantageous in giving a sharper upward thrust to the screen with the result that there is better impact action between the screen and the material being classified.

I claim:

l. Shake-screen apparatus including a base, a screen unit having at least one screen therein, mass-reaction means tending to oscillate the screen unit approximately in a desired oblique direction, and means for confining the oscillation of the screen unit to the desired direction including at least four substantially parallel tie links each pivoted to the screen unit and to the base about parallel axes perpendicular to the direction and parallel to the plane of the screen, the tie links extending upwardly from their pivotal connections with the base, the pivotal connection in each instance including a rubber bushing, and at least one of the pivotal connections having a bearing spread in the direction of the pivotal axis sufiiciently long to eliminate objectionable side sway and lateral movements of the screen unit, and a tie link on one side of the screen unit being rigidly connected with a tie link on the opposite side to maintain the two sides of the screen unit oscillating in phase with one another independently of structural rigidity of the screen unit, and resilient means acting other than by torque through the bushings, supporting the screen unit at a desired level at which the tie links are perpendicular to said direction of oscillation.

2. Shake-screen apparatus including a base, a screen unit having at least one screen therein, mass-reaction means tending to oscillate the screen unit approximately in a desired oblique direction, and means for confining the oscillation of the screen unit to the desired direction including at least four substantially parallel tie links each pivoted to the screen unit and to the base about parallel axes perpendicular to the direction and parallel to the plane of the screen, the pivotal connection in each instance including a rubber bushing, and at least one of the pivotal connections having a bearing spread in the direction of the pivotal axis sufliciently long to eliminate objectionable side sway and lateral movements of the screen unit, and a tie link on one side of the screen unit being rigidly connected with a tie link on the opposite side to maintain the two sides of the screen unit oscillating in phase with one another independently of structural rigidity of the screen unit, and resilient means supporting the screen unit at a desired level at which the tie links are perpendicular to said direction of oscillation.

3. Shake-screen apparatus including a base, a screen unit having at least one screen therein, mass-reaction means tending to oscillate the screen unit approximately in a desired oblique direction, and means for confining the oscillation of the screen unit to the desired direction including at least four substantially parallel tie links each pivoted to the screen unit and to the base about parallel axes perpendicular to the direction and parallel to the plane of the screen, the tie links extending upwardly from their pivotal connections with the base, the pivotal connection in each instance including a rubber bushing, and at least one of the pivotal connections having a bearing spread in the direction of the pivotal axis sufiiciently long to eliminate objectionable side sway and lateral movements of the screen unit.

4. Shake-screen apparatus including a base, a screen unit having at least one screen therein, mass-reaction means tending to oscillate the screen unit approximately in a desired oblique direction, and means for confining the oscillation of the screen unit to he e ired direction including at least four substantially parallel tie links each pivoted to the screen unit and to the base about parallel axes perpendicular to the direction and parallel to the plane of the screen, the tie links extending upwardly from their pivotal connections with the base, the pivotal connection in each instance including a rubber bushing, and at least one of the pivotal connections having a bearing spread in the direction of the pivotal axis sufiiciently long to eliminate objectionable side sway and lateral movements of the screen unit, and a tie link on one side of the screen unit being rigidly connected with a tie link on the opposite side to maintain the two sides of the screen unit oscillating in phase with one another independently of structural rigidity of the screen unit, and air cushion means acting directly between the screen unit and the base for supporting the unit and letting it oscillate both ways from a desired level at which the tie links are perpendicular to said direction of oscillation.

5. Shake-screen apparatus including a base, a screen unit having at least one screen therein, mass-reaction means tending to oscillate the screen unit approximately in a desired oblique direction, and means for confining the oscillation of the screen unit to the desired direction including at least four substantially parallel tie links each pivoted to the screen unit and to the base about parallel axes perpendicular to the direction and parallel to the plane of the screen, the tie links extending upwardly from their pivotal connections with the base, and at least one of the pivotal connections having a bearing spread in the direction of the pivotal axis sufficiently long to eliminate objectionable side sway and lateral movements of the screen unit, and a tie link on one side of the screen unit being rigidly connected with a tie link on the opposite side to maintain the two sides of the screen unit oscillating in phase with one another independently of structural rigidity of the screen unit, and resilient means supporting the screen unit at a desired level at which the tie links are perpendicular to said direction of oscillation, the screen being supported independently of the means oscillating the screen.

6. Shake-screen apparatus including a base, a screen unit having at least one screen therein, mass-reaction means tending to oscillate the screen unit approximately in a desired oblique direction, and means for confining the oscillation of the screen unit to the desired direction including at least four substantially parallel tie links each pivoted to the screen unit and to the base about parallel axes perpendicular to the direction and parallel to the plane of the screen, the tie links extending upwardly from their pivotal connections with the base, and at least one of the pivotal connections having a bearing spread in the direction of the pivotal axis sufiiciently long to eliminate objectionable side sway and lateral movements of the screen unit, and a tie link on one side of the screen unit being rigidly connected with a tie link on the opposite side to maintain the two sides of the screen unit oscillating in phase with one another independently of structural rigidity of the screen unit, and air cushion means acting directly between the screen unit and the base for supporting the unit and let-ting it oscillate both ways from a desired level at which the tie links are perpendicular to said direction of oscillation, the screen being supported independently of the means oscillating the screen.

7. Shake-screen apparatus including a'base, a screen unit having at least one screen therein, mass-reaction means tending to oscillate the screen unit approximately in a desired oblique direction, and means for confining the oscillation of the screen unit to the desired direction including at least four substantially parallel tie links each pivoted to the screen unit and to the base about parallel axes perpendicular to the direction and parallel to the plane of the screen, the tie links extending-upwardly from their pivotal connections with the base, the pivotal connection in each instance including a rubber b ushing,

and a tie link on one side of the screen unit being rigidly connected with a tie link on the opposite side to maintain the two sides of the screen unit oscillating in phase with one another independently of structural rigidity of the screen unit, and to prevent lateral movement of the screen unit, and resilient means supporting the screen unit at a desired level at which the tie links are perpendicular to said direction of oscillation, the screen being supported independently of the means oscillating the screen.

8. Shake-screen apparatus including a base, a screen unit having at least one screen therein, mass-reaction means tending to oscillate the screen unit approximately in a desired oblique direction, and means for confining the oscillation of the screen unit to the desired direction including at least four substantially parallel tie links each pivoted to the screen unit and to the base about parallel axes perpendicular to the direction and parallel to the plane of the screen, the tie links extending upwardly from their pivotal connections with the base, and a tie link on one side of the screen unit being rigidly connected with a tie link on the opposite side to maintain the two sides of the screen unit oscillating in phase with one another independently of structural rigidity of the screen unit; and pivotal means for mounting said rigidly'connected tie links on the frame having a combined spread along the axis at least equal to the width of the screen unit, and to prevent lateral movement of the screen unit, and resilient means supporting the screen unit at a desired level at which the tie links are perpendicular to said direction of oscillation, the screen being supported independently of the means oscillating the screen.

9. Shake-screen apparatus including a base, a screen unit having at least one screen therein, mass-reaction means tending to oscillate the screen unit approximately in a desired oblique direction, and means for confining the oscillation of the screen unit to the desired direction including at least four substantially parallel tie links each pivoted to the screen unit and to the base about parallel axes perpendicular to the direction and parallel to the plane of the screen, the tie links extending upwardly from their pivotal connections with the base, and a tie link on one side of the screen unit being rigidly connected with a tie link on the opposite side to maintain the two sides of the screen unit oscillating in phase with one another independently of structural rigidity of the screen unit; and pivotal means for mounting said rigidly connected tie links on the frame including rubber bushings at the two sides, having a combined spread along the axis at least equal to the width of the screen unit, and to prevent lateral movement of the screen unit, and resilient means supporting the screen unit at a desired level at which the tie links are perpendicular to said direction of oscillation, the screen being supported independently of the means oscillating the screen.

10. Shake-screen apparatus including a base, a screen unit having at least one screen therein, mass-reaction means tending to oscillate the screen unit approximately in a desired oblique direction, and means for confining the oscillation of the screen unit to the desired direction including at least four substantially parallel tie links each pivoted to the screen unit and to the base about parallel axes perpendicular to the direction and parallel to the plane of the screen, the tie links extending upwardly from their pivotal connections with the base, and at least one of the pivotal connections having a bearing spread in the direction of the pivotal axis sufliciently long to eliminate objectionable side sway and lateral movements of the screen unit, and air cushion means acting directly between the screen unit and the base for supporting the unit and letting it oscillate both ways from a desired level at which the tie links are perpendicular to said direction of oscillation, the screen being supported independently of the means oscillating the screen.

11. Shake-screen apparatus according to claim 10 in which the cushion means is provided with inflation connection means associated with the portion thereof which is stationarily associated with the base.

12. Shake-screen apparatus including a base, a screen unit having at least one screen therein, mass-reaction means tending to oscillate the screen unit approximately in a desired oblique direction, and means for confining the oscillation of the screen unit to the desired direction including at least four substantially parallel tie links each pivoted to the screen unit and to the base about parallel axes perpendicular to the direction and parallel to the plane of the screen, the tie links extending upwardly from their pivotal connections with the base, and at least one of the pivotal connections having a bearing spread in the direction of the pivotal axis sufliciently long to eliminate objectionable side sway and lateral movements of the screen unit, and air cushion means acting directly between the screen unit and the base for supporting the unit and letting it oscillate both ways from a desired level at which the tie links are perpendicular to said direction of oscillation, and assisting its reversal of movement; each air cushion including a pair of rims, a flexible casing carried by and between the rims, and a rigid annulus extending outwardly from a rim and positioned to restrain the natural axial flexing of the casing with respect to the rim to provide a more rapid increase of effective area of the air cushion on compression.

l3. Shake-screen apparatus including a base, a screen unit having at least one screen therein, means tending to confine the screen unit to movements partly upward and generally in one direction, means tending to oscillate the screen unit in that direction, and air cushion means acting directly between the screen unit and the base for supporting the unit and letting it oscillate both ways from a desired level at which the tie links are perpendicular to said direction of oscillation, and assisting its reversal of movement; each air cushion including a pair of rims, a flexible casing carried by and between the rims, and a rigid annulus extending outwardly from a rim and positioned to restrain the natural axial flexing of the casing with respect to the rim to provide a more rapid increase of effective area of the air cushion on compression.

References Cited in the file of this patent UNITED STATES PATENTS 1,130,656 Annable Mar. 2, 1915 2,144,382 Lincoln et al. Jan. 17, 1939 2,378,499 Rapp June 19, 1945 2,445,175 Hittson July 13, 1948 2,579,002 Johnson Dec. 18, 1952 2,700,470 De Gail Jan. 25, 1955 

